Attachment for video screens having dual optical active dereflection layers

ABSTRACT

An attachment for a video screen of a cathode ray tube of a monitor or TV receiver is constituted by a glass pane having on a front side, facing away from the video screen, a multilayer anti-reflective coating. If necessary, the glass pane on a rear side, facing towards the video screen, may incorporate an absorptive coating. The anti-reflective coating is limited to two active dereflective layers. One of said two layers is a metal layer of gold or a metal alloy with a gold content of more than 50% and with a thickness of 4 to 10 nm. The second active dereflective layer is of dielectric material with a refractive power of n&lt;1.8 and constituting an interference layer which faces away from the glass pane and which is essentially absorption-free and forms an anti-reflective layer for the visible region of the spectrum.

FIELD OF THE INVENTION

The invention concerns an attachment for video screens or the like, suchas cathode ray tubes of monitors, TV sets or the like, with a glass panewhich has on its front side, facing away from the video screen or thelike, a multilayer anti-reflective coating and if necessary on its rearside, facing towards the video screen or the like, a reflection-reducingcoating and in particular an absorbent coating (or the like).

BACKGROUND OF THE INVENTION

In the case of computer monitors, TV sets and the like, there isfrequently a need for reflection reduction of the cathode ray tubesused. This aim can be achieved for example by etching the surface,coating the tube or also by means of anti-reflectively coatedattachments. The coating used for such attachments should have a lowsurface resistance so as to be able to act as a shield againstelectromagnetic radiation. For this purpose, an electrical surfaceresistance of less than 100 ohms is generally necessary.

Hitherto, the following have been used as blooming layers forattachments: single layers, with the disadvantage of residualreflection, of an intense colour effect as well as deficient electricalconductivity; double layers with the disadvantages of an intense coloureffect and low conductivity; dielectric multilayer systems with thedisadvantages of high production cost and high electrical resistance;and conductive multilayer systems which are particularly costly toproduce and are thus expensive.

Double layer systems for attachments rendering it possible to achievesatisfactory reflection elimination over wide regions of the visiblespectrum are not known. To the contrary, the use of such simple layersystems is always accompanied by an intense colour effect. To reduce thecolour cast therefore, multilayer systems are used, which result in muchhigher production cost.

From DE-OS 36 29 996, an attachment of the generic type is known, wherethe glass pane, as also is the case with the invention, can consisteither of inorganic glass, in particular of toughened safety glass, oralso of plastic, i.e. organic glass, incorporates on the back thereof,an absorption coating of for example chromium and on the front ananti-reflective coating of two or three layers of differing refractiveindex, whereby the neutrality of the colour effect, as well as theproduction cost leaves much to be desired.

From US-PS 2 366 687, an anti-reflective coating for glass panes isknown, where a metal layer of a material with a high reflection but lowabsorption factor and a dielectric interference layer of for exampleSiO₂ are applied consecutively to the glass panes. Usable metals arespecified as copper, silver, rhodium, aluminium or other similarlystable metals with the aforementioned properties. The use of such ananti-reflective coating for attachments of the generic type leads, ifmetals other than copper are chosen, to an undesirably high coloureffect, whilst the use of copper is ruled out on account of its lack ofstability for front coatings of attachments of the type in questionhere.

In GB-PS 826 754, electrically conductive coatings on glass panes aredescribed which as a metal layer, can contain alternatively a gold,silver, nickel or iron layer and as part of an outer anti-reflectivelayer can contain SiO₂ for example, whereby the intense colour effectoccurring except when using gold can be taken into account in theapplication stated there and no indication is given as to how to producea neutral colour effect by suitable selection of material.

A similar attachment as is described in accordance with the genericstate of the art in DE-OS 39 41 797, with the problems explained withthe aid of the above mentioned Patent Specification. DE-PS 21 38 517concerns a thermal insulation pane with a coating of gold and highrefractive index dielectric material, where the use of such a coatingwith an attachment of the generic type would not permit the desiredreflection reduction.

SUMMARY OF THE INVENTION

The purpose of the invention is to provide an attachment of the generictype whose anti-reflective coating with cost-effective productionpermits a reduction of the light reflection factor of the front of theglass pane from approx. 4% to less than 0.5%, is to a large extentneutral in colour and possesses a surface resistance of less than 100ohms.

This problem is solved by the invention by the anti-reflective coatingcomprising a metal layer of gold or a metal alloy with a gold content ofmore than 50% with a thickness of 4 to 10 nm and an interference layerlocated on its side facing away from the glass pane which is essentiallyabsorption-free, forming an anti-reflective layer for the visible regionof the spectrum, of dielectric material with a refractive power ofn<1.8.

It can be provided for the thickness of the metal layer being 5 to 7 nm.

Furthermore, the invention proposes that the optical thickness of theinterference layer should be 60 to 140 nm.

According to a further embodiment of the invention, it can be providedfor the interference layer consisting of at least a metal oxide ormetalloid oxide.

It can be provided for the interference layer consisting of SiO₂.

A further embodiment of the invention is characterized by the fact that(in each case) an adhesive layer is located between the glass pane andthe metal layer and/or between the metal layer and the interferencelayer.

NiCr, silicon, indium oxide and/or indium-tin oxide may be used asmaterial for the adhesive layer(s).

The invention also proposes that at least a part of the layers of theanti-reflective coating is produced by magnetron cathode sputtering.

The invention is based on the surprising principle that as a result ofthe interplay between the metal and the interference layer according tothe invention, an unexpectedly neutral-coloured reflection eliminationeffect for a double layer system can be achieved. This effect isapparently based on the characteristic of the complex refractive indexof gold which is unusual for metals, which is characterized by the factthat its real component decreases significantly as a monotonic functionin the region of the visible spectrum.

No inducement for such a choice of material was gathered from the stateof the art discussed at the beginning because although US-PS 2 366 687mentions copper, whose refractive index possesses a characteristicsimilar to that of gold, in comparison as regards effect with silver,rhodium and aluminium, their refractive index is quite different andbehaves in a way which is useless for the invention, whilst GB-PS 826754 describes gold as acting in the same way as inter alia silver,nickel and iron, whose refractive index characteristic also rendersthese metals unsuitable for the purpose of the invention. DE-PS 21 38517 on the other hand specifies the use of gold in combination with ahigh refractive index anti-reflective layer, whilst the purpose of theinvention can only be achieved by a combination of the gold layer andthe low refractive index interference layer in the sense of theanti-reflective coating claimed.

It lies within the scope of the invention to embed the gold or goldalloy layer on both sides in thin adhesive layers in known fashion. Whenmanufacturing the layer system by means of magnetron cathode sputtering,as is provided for more advantageously, it is advisable to use thinadhesive layers of NiCr, silicon, indium oxide or indium-tin oxide, asthe adhesion of the anti-reflective coating can be significantlyimproved thereby.

Further features and advantages of the invention are shown by thespecification below, in which embodiments are explained in detail withthe aid of the schematic drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a first embodiment of an attachmentaccording to the invention sectioned perpendicular to the plane of theglass pane used;

FIG. 2 is a sectional view of a modified representation as per FIG. 1 ofa second embodiment of an attachment according to the invention;

FIG. 3 is a plot of the light reflection factor of the attachment as perFIG. 2 as a function of the wavelength;

FIG. 4 is a plot of the characteristic of the real component and of theimaginary component of the refractive index of gold as a function of thewavelength, and

FIG. 5 is a plot of the light reflection factor as a function ofwavelength with respect to a second embodiment of the invention,according to FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT

In the case of the embodiment shown in FIG. 1, a gold layer 12 with athickness of 5 nm and an essentially absorption-free interference layer14 of SiO₂ with a thickness of 7 nm have been applied consecutively bymagnetron cathode sputtering to a transparent glass pane 10, consistingin the example shown of a float glass pane of soda lime silicate glass 6mm thick.

In the case of the embodiment of FIG. 2, where the glass pane 10 againconsists of a float glass pane of soda lime silicate glass with athickness of 4 mm, an NiCr adhesive layer 16 with a thickness of 0.5 nm,a gold layer 12 with a thickness of 6 nm, an In₂ O₃ adhesive layer 18doped with SnO₂ with a thickness of 4 nm and an interference layer 14 ofSiO₂ with a thickness of 60 nm are consecutively applied to the glasspane 10.

In detail, the manufacture of the attachment in accordance with FIG. 2was carried out as follows:

In a vacuum coating plant which was equipped with coating devices formagnetron cathode sputtering, the following layers were appliedconsecutively to the glass pane 10, a float glass pane of soda limesilicate glass of 4 mm thickness of format 40 cm×40 cm: the adhesivelayer 16 in the form of an NiCr adhesive layer 0.5 nm thick bysputtering of an NiCr (80/20) target in argon atmosphere at a pressureof 1.5* 10⁻¹ Pa, the gold layer 12 of 6 nm thickness by sputtering agold target in argon atmosphere at a pressure of 1.5*10⁻¹ Pa, theadhesive layer 18 in the form of an In₂ O₃ adhesive layer doped withSnO₂ with a thickness of 4 nm by reactive sputtering of the In90/Sn10target in argon/oxygen atmosphere at a pressure of 3.5*10⁻¹ Pa andfinally the interference layer 14 in the form of an SiO₂ 60 nm thick byreactive sputtering of an Si target in argon/oxygen atmosphere at apressure of 1.5 Pa. The back of the glass pane 10, not shown in thedrawing, was coated with a light absorbing Cr layer of a thickness suchthat the transmission of an uncoated float glass pane was reduced byapprox. one third.

The coated pane possessed a light reflection factor with normal lightType A of 0.21%. Transmission was 55%. The spectrum loci in reflection,measured at L, a, b colour system (according to R. S. Hunter,Photoelectric Color Difference Meter, in J. Opt. Soc. Am. 48 (1958), p.985 et seq) were a=0.5 and b=-1.0. The electrical surface resistance ofthe front anti-reflective coating was 30 ohms.

In FIG. 3, it can be seen that the light reflection factor of the paneover the entire visible range of the spectrum is clearly lower than thatof an uncoated pane.

FIG. 4 shows that the real component of the complex refractive index ofgold decreases significantly as a monotonic function over the region ofthe visible spectrum, to which the surprising effect of the attachmentaccording to the invention, in combination with the low refractive indexinterference layer used, is significantly attributable.

FIG. 5 shows that, by optimizing layer arrangement and layer dimension,i.e. thickness, according to the second embodiment as shown in FIG. 2,the optical characteristics which have been shown to be very good withrespect to the first embodiment according to FIG. 2 can be exceeded. Thelight reflection factor is, in comparison with FIG. 3, practically inthe entire represented wavelength range, lower. The neutrality in colouris further improved at the same time.

The features of the invention disclosed in the foregoing specification,in the drawing and in the claims can be essential both individually andalso in any combination for the implementation of the invention in itsvarious embodiments.

I claim:
 1. Video screen attachment for attachment to a cathode ray tubeof a monitor or TV receiver comprising:a glass pane having a first sidefacing away from a video screen ad an opposite rear side, a multilayeranti-reflective coating of no more than two active dereflective layerson said first side of said glass pane comprising:(1) a metal layer (12)of gold or a metal alloy of gold content in excess of 50% of a thicknessof 4 to 10 nm, and (2) an interference layer (14) of a dielectricmaterial with a refractive power of n<1.8 on said metal layer on theside facing away from said glass pane (10), which is essentiallyabsorption-free and forming an anti-reflective layer for the visibleregion of the spectrum.
 2. Attachment in accordance with claim 1,further comprising a light absorbent coating on the rear side of saidglass pane.
 3. Attachment in accordance with claim 1, characterized bythe fact that the thickness of the metal layer (12) is 5 to 7 nm. 4.Attachment in accordance with claim 1, characterized by the fact thatthe optical thickness of the interference layer (14) is 60 to 140 nm. 5.Attachment in accordance with claim 1, characterized by the fact that heinterference layer (14) comprises a metal or metalloid oxide. 6.Attachment in accordance with claim 5, characterized by the fact thatthe interference layer (14) consists of SiO₂.
 7. Attachment inaccordance with claim 1, characterized by the fact that an adhesivelayer (16, 18) is located between the glass pane (10) and the metallayer (12) and between the metal layer (12) and the interference layer(14).
 8. Attachment in accordance with claim 7, wherein said adhesivelayer is one material form the group consisting of NiCr, silicon, indiumoxide and indium-tin oxide.
 9. Attachment in accordance with claim 1,characterized by the fact that at least a part of the layers (12, 14,16, 18) of the antireflective coating is produced by magnetron cathodesputtering.